This invention relates generally to the field of rotary switches. More specifically, it relates to a rotary encoding switch, of the type having a stationary contact spring element with multiple spring contact fingers that are urged axially into engagement with selected coded terminal elements by an arrangement of axial cams on the underside of a rotor.
Rotary encoding switches, of the type mentioned above, are known in the art. See, for example, U.S. Pat. No. 4,400,597--Bruder et al.; U.S. Pat. No. 5,008,498--Yamazaki; and U.S. Pat. No. 5,010,214--Yamazaki. In such switches, a stationary spring contact, or "spider", having multiple spring contact arms, is fixed within a housing between a rotor and a plurality of fixed coded electrical terminals, so that the spring arms are axially movable to make and break electrical contact with the terminals. A rotor is provided with a plurality of axially-extending camming elements on the surface facing the spider. As the rotor is turned, the camming elements are brought into and out of engagement with cam follower structures on each of the contact arms, whereby the arms are displaced axially into contact with a selected terminal as the rotor is turned, in accordance with the pattern of the camming elements. When the cam follower structure on an arm is not engaged by a cam, the resilience of the arm causes it to move axially out of engagement with the terminal, thereby breaking contact therewith.
There has been a long term trend for higher degrees of miniaturization of electronic components. Consistent with that trend, components such as rotary switches have been substantially reduced in size, and further size reductions are still demanded. For example, surface mounted components, including rotary switches, are now commonly made smaller than 10 mm on a side, and components of as little as 4 to 5 mm on a side are in increasing demand.
The structure of the prior art rotary switches, of the type described above, makes such ultra-miniaturization difficult to achieve while maintaining performance criteria, such as accuracy and reliability. For example, the device described in the above-referenced patent to Bruder et al. employs a spider having radial contact arms of substantially uniform total length, each having a single cam follower tab. Each of the tabs is located at a different unique radius, for actuation by a cam lobe located at the corresponding radius on the facing surface of the rotor. Electrical contact between the contact arms and the switching terminals occurs at the ends of the contact arms. This radial contact arm structure, and the need to have one contact arm dedicated to each camming radius, lead to an inefficient use of space that imposes limits on the degree of miniaturization that can be achieved.
A more efficient use of space is obtained in the devices described in the above-referenced patents to Yamazaki. These devices employ a stationary contact or spider having the configuration shown in FIG. 1 attached to the present specification. As shown, the prior art spider 10 includes a plurality of contact arms 12a, 12b, 12c, 12d, and 12e, arranged circumferentially, rather than radially. Each contact arm 12a--12e is located at a different radial distance from the center of the spider, and is actuated by a rotor-mounted camming element (not shown) that is located at the same radial distance from the center of the rotor, and that operates on its associated contact arm through a cam follower projection 14 on the arm.
In other words, each camming element, at its unique distance from the center of the rotor, operates on a single contact arm located at the same radial distance from the center of the spider. In a binary coded switch, each binary bit (i. e., 1, 2, 4, 8, etc.), is defined by a unique camming element operating only on its associated contact arm. Thus, each bit requires its own unique operational camming element/contact arm radius, thereby requiring either spiders and rotors of larger radii, or smaller (and more delicate) contact arms and camming elements, as the number of bits is increased. In addition, for any given number of bits, size can be reduced only by reducing the width of the contact arms and reducing the size and spacing between the camming elements, thereby possibly compromising durability and reliability.
In short, if further miniaturization is desired, one must either reduce the width of each contact arm, or limit the number of contact arms. If the former course action is employed, durability and reliability may be compromised, and manufacturing costs may be increased. If the latter strategy is used, the number of switching values may be limited.
It would therefore be desirable, if maximum efficiency in space utilization is the goal (as it is in ultra-miniaturization), to arrange the contact arms and the associated camming structures so that more than one contact arm is located at a single radial distance from the center of the spider, so as to be actuated by one or more camming structures located at that same radial distance from the center of the rotor.